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BQ34Z100: Inadvertent Charging

Sagar Sadasivan
Prodigy 205 points
Part Number: BQ34Z100
Other Parts Discussed in Thread: , BQ77905

Customer was wondering whether a high voltage on clock or data could leak thru the FET body diode on the bq34z100 and charge the cell? Please see the Maxim App Note for more information on the concern.

Gas Gauge Placement maxim AN123.pdf

  • 0
    TI__Mastermind 25955 points
    Hi Sagar,

    This app note discusses a potential path if your gauge is placed 'upstream' of your protection FETS. Please do not place the bq34z100-G1 or any other gauge sense circuitry 'upstream' of your protection FETS.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Intellectual 855 points

    Bryan,

    Is the diagram on page 1 of the SLUSBZ5B incorrect?

    Thanks,

    Larry Norman

  • 0 in reply to Larry Norman
    TI__Mastermind 25955 points
    Hi Larry,

    The diagram on page 1 of SLUSBZ5B is a simplified schematic of one example implementation of the device. The bq34z100-g1 is a multi-chemistry device - different chemistries have different industry standards for protection.

    I cannot speak to the faults and safety concerns with respect to the DS2438 mentioned in the above linked app-note.

    If using a lithium ion setup:

    Figure 17 in the bq34z100-G1 datasheet may be a preferable starting point for the bq34z100-g1 implementation combined with Figure 34 of the bq77905 datasheet ( www.ti.com/.../bq77905.pdf ) wherein the lowside CHG and DSG FETs are located between the cells and the bq34z100-G1.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Intellectual 855 points

    Hi Larry,

    I believe the following diagram should help.  Please replace the /PRES or SMBC/SMBD pins shown on the gauge/battery host uC block below with general I/O or comms lines, such as HDQ, I2C, or alert pins for the bq34z100-G1.

    Sincerely,
    Bryan Kahler

  • 0 in reply to Larry Norman
    TI__Mastermind 25955 points
    Hi Sagar and Larry,

    Haven't heard back since this answer was suggested - hope the issue is resolved. If not, please let us know.

    If this answer resolved the issue, please hit the green 'resolved' button to help improve question/answer searchability on the forums. Thank you!

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Intellectual 855 points

    Hello Bryan,

    Thanks for the input. I did not get a notification of your previous post, or I would have responded earlier. It looks like my second post on 08/17 has been deleted.

    But it looks like you have answered the question.

    Thanks,

    Larry

  • 0 in reply to Larry Norman
    TI__Mastermind 25955 points
    Hi Larry,

    Excellent. Could you please hit the green 'resolved' button so this question/answer pair is easier for other customers to find?

    Thanks!

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Intellectual 855 points
    Hello Bryan,

    Sagar started the thread for me, so I am unable to close it...